Gas generator for actuating vehicle passenger constrainer

ABSTRACT

A gas generator for actuating a vehicle occupant restraint device, including a first hollow body with a bottom and sides, gas generants filled densely in the first hollow body, an electric ignitor formed by housing igniting agents in a second hollow body with a bottom and sides, and closing the second hollow body with a plug, and a holder positioning the second hollow body in a center of the first hollow body and fixing the first hollow body while holding the plug of the electric ignitor. Particularly, a ratio of an empty space to a full volume of a space partitioned by an inner surface of the first hollow body, an outer surface of the second hollow body, and the holder is less than 20% by volume.

TECHNICAL FIELD

The present invention relates to a gas generator for actuating vehicleoccupant restraint devices such as pretensioner belts.

BACKGROUND ART

A pretensioner belt is a vehicle occupant restraint device for detectingcollision and subsequently tightening a seat belt. For tightening seatbelts, there has been normally employed a mechanism of tightening seatbelts by gas pressure of a gas generator.

Such gas generator includes a first hollow body with a bottom and sides,gas generants filled in the first hollow body, an electric ignitor, anda holder. The electric ignitor is formed with a second hollow body witha bottom and sides, igniting agents housed in the second hollow body,and a plug closing an opening portion of the second hollow body. Theholder positions the second hollow body in the center of the firsthollow body, holding the plug of the electrical ignitor. The holderfixes the second hollow body in the first hollow body, closing theopening portion of the first hollow body.

In this kind of as generator, two parts are prepared. One is a firsthollow body filled with gas generants. The other is an electric ignitorfixed to a holder and shaped so as to project from the holder. It isdifficult to put the holder into the first hollow body without leavingan excessive empty space because of the cylindrical configuration of thewas generator.

Therefore, when the electric ignitor is actuated and the gas generantsare ignited, increase in inner pressure by ignition in the first hollowbody is slowed because of the excessive empty space in the first hollowbody. As a result, a rupture of a rupture member of the first hollowbody is delayed and there is an adverse possibility that desiredperformance cannot be obtained.

Generally, a permissible ignition delay period (the period of timebetween a start of current flow to the electric ignitor and a start ofdischarging gas from the gas generator) is within 2 ms for the seat beltpretensioners of automobiles. When the ignition delay period is morethan 2 ms, an occupant restraint performance cannot be shownsufficiently.

when excessive empty space exists, a size of a gas generator is extendedby the empty space. Further, because the gas generants are not fixed,powdering thereof by vibration of a vehicle is also concerned. When sucha powdering phenomenon occurs, a combustion velocity of the gasgenerants becomes extremely fast, and then the gas generator maypossibly be damaged.

Hence, Japanese Patent Application Laid-Open No. Hei 8-207694 hasdisclosed a cup-shaped filling cylinder for filling gas generantswithout leaving an empty space. The second hollow body of the electricignitor projects inwardly from the bottom of the cup-shaped fillingcylinder. The cup-shaped filling cylinder opens upwardly from the secondhollow body of the electric ignitor.

First, in the gas generators having the above-mentioned cup-shapedfilling cylinder, the gas generants are filled in the cup-shaped fillingcylinder thereof without leaving an empty space. Then, the first hollowbody is put on the cup-shaped filling cylinder to cover the openingportion of the cup-shaped filling cylinder. When the gas generants arefilled in the first hollow body in this way, it is possible to fix thesecond hollow body of the electric ignitor in the first hollow bodywithout forming an excessive empty space therein.

However, a filling cylinder needs to be newly provided in this case. Asa result, in addition to an increase in the number of components,simplification of the manufacturing process cannot be expected.

It is an object of the present invention to provide a gas generator foractuating vehicle occupant restraint devices having a small number ofcomponents and excellent ignitability, and being capable ofminiaturization.

SUMMARY OF THE INVENTION

As a result of eager investigation of the present inventors to solve theabove-mentioned problem, the present inventors have found that it isimportant to regulate a ratio of an empty space to an inner volume ofthe first hollow body to achieve the present invention.

The present invention relates to a gas generator for actuating a vehicleoccupant restraint device comprising a first hollow body with an end anda side wall, gas generants densely filled in the first hollow-body, anelectric ignitor formed by housing igniting agents in a second hollowbody with an end and a side wall then closing the second hollow bodywith a plug, and a holder positioning the second hollow body in thecenter of the first hollow body while fixing the first hollow body andholding the plug of the electric ignitor.

In a first gas generator of the present invention, a ratio of an emptyspace to a volume of a space partitioned by an inner surface of thefirst hollow body, an outer surface of the second hollow body and theholder (hereinafter it is described as full volume) is less than 20% byvolume. The empty space and the ratio of the empty space by volume arecalculated by using

empty space=full volume−filling volume  (1)

ratio of an empty space by volume=(empty space volume/fullvolume)×100  (2)

Fundamentally, a space that exists among the particles of filled gasgenerant compositions is not regarded as a gap. And the filling volumemeans a necessary volume for gas generants filled in a dense state tosubstantially exist in the full volume.

According to the first gas generator of the present invention, becausethe ratio of the empty space to the full volume of the first hollow bodyis less than 20%, the first hollow body is substantially full of the gasgenerants. Therefore, ignition energy of the electric ignitor istransmitted efficiently and the time for raising for inner pressure ofthe first hollow body is shortened.

Accordingly, in the case an electrical ignitor with small ignition poweris used, there is no possibility that an ignition delay occurs. Inaddition, because the first hollow body is substantially full of the gasgenerants, the gas generants are prevented from being powdered byvibration of vehicles. To ensure the above-mentioned action, it ispreferable that the ratio of empty space is less than 15%, furtherpreferably, less than 10%.

The conventional cup-shaped filling cylinder is not necessary, therebyproviding reduction of the number of components.

A second gas generator of the present invention is characterized in thatthe gas generants are powdery or granulated and filled in a compressedstate, in addition to the above-mentioned characteristics of the firstgas generator. As examples of compressible gas generants, there arepowdery or granulated non-azide gas generants, propellant gas generantsand the like.

According to the second gas generator of the present invention, the gasgenerants are powdery or granulated. Therefore, the gas generants can befilled without leaving space and a ratio of the empty space can beeasily predetermined. Because the gas generants are filled in acompressed state, the filling density is heightened and the gasgenerator is miniaturized. Combustion velocity can be adjusted byadjusting a filling weight and a compression height (i.e. a height of asurface formed with the filled agents). It is preferable that theaverage particle size of material of the powdery or granulated gasgenerants is adjusted so as to fall into the range of 10-300 μmincluding 10 μm and 300 μm. It is preferable that the compression degreeof the gas generants falls into the range of 30-100% including 30% and100%. The compression degree. of the gas generants is regarded as 100%when the gas generants are compressed with the density equal to the truedensity.

The powdery or granulated gas generants, adjusted to be in thepredetermined range mentioned above, can be hardened into apredetermined form by compression at a predetermined pressure.

A third gas generator of the present invention is characterized in thata part of the full volume is filled with a spacer 7 inserted between anouter surface of the side wall of the second hollow body 4 a and aninner surface of the side wall of the first hollow body 2, in additionto the above-mentioned characteristics of the first or the second gasgenerator.

According to the third gas generator of the present invention, an emptyspace between the outer surface of the side wall of the second hollowbody 4 a and the inner surface of the side wall of the first hollow body2 can be filled with the spacer 7. Therefore, even if a form of the gasgenerator cannot be modified for reason of a design of a vehicleoccupant restraint device, it is possible to lower the ratio of theempty space. As a result, the first hollow body 2 is substantially fullof the gas generants 6, thereby an excellent ignitability is obtained.

An empty space in this gas generator is calculated by using

 empty space=full volume−(filling volume+volume of a spacer)  (1′)

Further, when the length of the spacer is adjusted according to thelengths of the first hollow body and the second hollow body, it ispossible to adjust the full length of the gas generator withouteliminating an excellent ignitability.

Particularly, a configuration where the spacer is located around theelectric ignitor, is desirable. The electric ignitor may be formed so asto include the spacer depending on circumstances. Thereby, ignitionenergy is concentrated on the gas generants, and the ignitability ismaintained. The spacer remains fixed on the electric ignitor after thegas generator is actuated.

Rigid material is desirable for the spacer. For example, the spacer ismade of aluminum, plastic, glass fiber, and the like and formed into adoughnut shape, a mesh shape, and the like. When the spacer is made of agas generant composition with the same form as mentioned above, it ispossible to increase the output of the gas generator.

A fourth gas generator of the present invention is characterized in thatthe gas generants are compressed in advance and filled in the firsthollow body so that a concavity, in at which the second hollow body isinserted, is formed, in addition to the above-mentioned characteristicsof the first or the second gas generator.

According to the fourth gas generator of the present invention, the gasgenerants are compressed in the first hollow body in advance so that theconcavity, in which the second hollow body is inserted, is formed.Therefore, when the second hollow body is inserted into the first hollowbody, the second hollow body is surrounded by the gas generants. Theignition energy of the electric ignitor is transmitted to the gasgenerants surrounding the second hollow body without waste. Therefore,there is no possibility that an ignition delay occurs. For compressingthe gas generants into a concave shape in the first hollow body, convexcompressing tools may be used.

A fifth generator of the present invention is characterized in that gasgenerants that are incompressible or hard to compress are filled denselyin the first hollow body and a part of the full volume is filled withthe spacer inserted between the outer surface of the side wall of thesecond hollow body and the inner surfaces surface of the side wall ofthe first hollow body, in addition to the above-mentionedcharacteristics of the first gas generator.

In the gas generator of the present invention described above, theexcessive empty space in the first hollow body can be reduced, therebyreducing an ignition delay of the gas generator. Further, the gasgenerants are prevented from being powdered by vibration of vehicles.Thus, the gas generator of the present invention is excellent inignitability and reduced in size though it is manufactured in amanufacturing process almost the same with the conventional one.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the first embodiment of the presentinvention;

FIG. 2 is a sectional view of the second embodiment of the presentinvention;

FIG. 3 shows the relationship of the ratio of the empty space by volumeand ignition delay period of the gas generator.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described below withreference to the drawings.

In FIG. 1 a gas generator 11 includes a first hollow body 2 with an endand a side wall, gas generants 6 filled in the first hollow body 2, anelectric ignitor 4, a holder 1, and a spacer 7.

In FIG. 1 a gas generator 11 includes a first hollow body 2 with abottom and sides, gas generants 6 filled in the first hollow body 2, anelectric ignitor 4, a holder 1, and a spacer 7.

An end of the first hollow body 2 is provided with a rupture portion 2 athin in wall thickness. The first hollow body 2 is press-formed so as tohave two sections consisting of a small diametral portion on an end sideand a large diametral portion which is a main portion. An end of themain portion is bent to be a flange 2 b.

The electric ignitor 4 has a second hollow body 4 a with an end and sidewall, igniting agents 4 b housed in the second hollow body 4 a, a plug 4c to close an opening portion of the second hollow body 4 a, and twopins 4 d standing on the plug 4 c. The two pins 4 d are connected to abridge wire (not shown) being in contact with the igniting agents 4 b.

The holder 1 fixes the first hollow body 2 positioning the second hollowbody 4 a in the center of the first hollow body 2. Further, the holder 1supports the plug 4 c by a caulking portion 1 b with an O-like ring 5around an outer circumference of the plug 4 c. The O-like ring 5 isemployed for use in sealing. The holder 1 projects a part of the secondhollow body 4 a of the electric ignitor 4 into the first hollow body 2,and allows parts of the pins 4 d to be connected to a connector (notshown).

An insulation ring 3 is fitted to a hole 1 a in back of the holder 1 toensure insulation. The caulking portion 1 b for supporting the plug 4 cis inserted in the opening portion of the first hollow body 2. By thecaulking portion 1 c of the holder 1 on the flange 2 b of the firsthollow body 2, the first hollow body 2 is fixed on the holder 1 in asealed condition.

A space partitioned by an inner surface of the first hollow body 2, anouter surface of the second hollow body 4 a and the holder 1 is capableof housing gas generants. The gas generants 6 and the spacer 7 arelocated in this space.

The spacer 7 is, for example, in a cylindrical shape, where a diameterof the inner circumference thereof is substantially the same as thediameter of the outer circumference of the second hollow body 4 a and adiameter of the outer circumference thereof is substantially the same asthe diameter of the inner circumference of the main portion of the firsthollow body 2. The spacer 7 is inserted between the outer surface of theside wall of the second hollow body 4 a and the inner surface of theside wall of the first hollow body 2.

A length of the cylindrical spacer 7 is determined so that thelater-described ratio of the empty space by volume is less than 20%, inconsideration of the later-described filling volume of the gasgenerants.

In the case that the gas generants 6 are incompressible or hard tocompress e.g. smokeless powder or press-formed non azide gas generants,the gas generants are densely filled in the first hollow body 2 on theend side thereof. In the case that the gas generants 6 are compressibleand powdery or granulated, the gas generants are densely filled in thefirst hollow body 2 on the end side thereof in a condition hardened by acompression. The dimension h in the drawing refers to a distance betweenthe bottom of the first hollow body 2 and the filling surface (i.e. thesurface formed with filled agents).

It is possible to increase a weight of the gas generants 6 by shorteningthe length of the spacer 7. Further, when the spacer 7 is made of a gasgenerant composition, a space for housing the gas generants of the firsthollow body 2 is not wasted and the amount of generated gas can beincreased.

The volume of a space, which is partitioned by an inner surface of thefirst hollow body 2, an outer surface of the second hollow body 4 a andthe holder 1 and capable of housing the gas generants, constitutes afull volume.

According to the present invention, a volume and a form of the spacer 7and a filling volume of gas generants are determined so that the ratioof an empty space, which is not filled with the spacer 7 and the gasgenerants, to the full volume is less than 20% by volume, preferablyless than 10%.

Fundamentally, a space that exists among the particles of filled gasgenerant compositions is not regarded as a gap. And the filling volumemeans a necessary volume for gas generants filled in a dense state tosubstantially exist in the full volume.

Specifically, the filling volume of the gas generants filled in thefirst hollow body 2 on the end side thereof, shown in FIG. 1, iscalculated in consideration of a distance h between the end of the firsthollow body 2 and the filling surface (i.e. a surface formed with thefilled agents), an inner diameter of the first hollow body 2, and anouter diameter of the second hollow body 4 a.

A volume of the empty.space and the ratio thereof are calculated byusing

volume of an empty space=full volume−(filling volume+volume of aspacer)  (1′)

ratio of an empty space by volume=(empty space volume/fallvolume)×100  (2)

In the gas generator where the gas generants 6 and the spacer 7 arelocated, it is possible that the ratio of the empty space to the fullvolume is less than 20%, further, less than 10%. The full volume is avolume of the space partitioned by the inner surface of the first hollowbody 2, the outer surface of the second hollow body 4 a and the holder1.

Particularly, in the case that the gas generants are incompressible orhard to compress e.g. smokeless powder or press-formed non azide gasgenerants, the gas generants cannot be hardened into a predeterminedshape by a compression so as to fit a space for housing the gasgenerants of the gas generator. Therefore, it is preferable to use thespacer so as not to form an excessive empty space.

The above-mentioned gas generator is manufactured by the followingsteps. In the case that the gas generants are incompressible or hard tocompress e.g. smokeless powder or press-formed non azide gas generants,the gas generants are densely filled in the first hollow body 2 on theend side thereof. In the case that the gas generants 6 are compressibleand powdery or granulated, the gas generants are densely filled in thefirst hollow body 2 on the end side thereof in the state hardened bycompression.

The electric ignitor 4 is supported by the holder 1 and the spacer 7 isfitted around the outer circumference of the second hollow body 4 a ofthe electric ignitor 4. Then, the holder 1 is fitted to the first hollowbody 2 and fixed by the caulking portion 1 c. Thus, the gas generator ofwhich inner space is regulated, is manufactured in a process almost thesame with the conventional one.

FIG. 2 shows a gas generator without a spacer, in which the gasgenerants 6 are compressed to be concave to fit the second hollow body 4a. The gas generants 6, which are powdery or granulated andcompressible, are suitable. The portions functioning the same way withthose of FIG. 1 are referred to by the same reference numerals and thedescription is omitted.

The gas generants 6, which are compressible and powdery or granulated,are densely filled in the first hollow body 2 on the end side thereof inthe state hardened by a compression to have a concavity 6 a to which thesecond hollow body 4 a of the electric ignitor 4 is just fitted. Thedimension H in the drawing refers to a distance between the bottom ofthe first hollow body 2 and the filling surface (i.e. a surface formedwith the filled agents).

In the embodiments of the present invention, a filling volume of the gasgenerants 6 is determined so that the ratio of an empty space, which isnot filled with the gas generants 6, to the full volume is less than 20%by volume, preferably less than 10%.

In the case that the gas generants 6 are compressed in the first hollowbody 2 in advance to be concave to fit the second hollow body 4 a asdescribed above, the second hollow body 4 a is surrounded by the gasgenerants simply by inserting the second hollow body 4 a in the firsthollow body 2 and fixing by the caulking portion 1 c of the holder 1.Therefore, the inner empty space of the gas generator is reducedcompared to the conventional one.

The degree of compression of the gas generants is regarded as 100% whenthe gas generants are compressed to a density equal to a true densitythereof. In the gas generator of the present invention the degree ofcompression preferably falls in a range of 30-100%, including 30% and100%, so that the gas generants can be compressed into a predeterminedform. Concretely, the compression degree is calculated by using

compression degree [%]=(weight of gas generants per 1 cm³ of a fillingvolume/true density of gas generants)×100

In the following, the examples of the present invention will bedescribed in detail. All members included in the gas generators employedin the following examples and comparative examples, such as electricignitors, O-like rings or holders, are of the same standard or type.

EXAMPLE 1

In the gas generator shown in FIG. 2, the gas generants containing 33.8%by weight of 5-aminotetrazole, 30.5% by weight of ammonium perchlorate,31.0% by weight of strontium nitrate, and 4.7% by weight of synthetichydrotalcite were employed. The true density was 2.18 g/cm³. The gasgenerants were powdery, o with a particle mean diameter of 50 μm, andcompressible.

Gas generants weighing 1.9 g were weighed and filled in the first hollowbody. Then, the gas generants were compressed for forming a concavityuntil the filling volume was 2.11 cm³. The full volume of the gasgenerator is 2.3 cm³. The empty space calculated by the equation is 0.19cm³ and the ratio is 8.3% by volume. The weight of the gas generants per1 cm³ of the filling volume is 0.9 g and the compression degree is41.3%.

FIG. 3 shows the ratio of the empty space by volume and ignition delayof the gas generator obtained in Example 1.

EXAMPLE 2

In the gas generator shown in FIG. 2, the same gas generants as thoseused in the Example 1 were employed. The true density was 2.18 g/cm³.The gas generants were powdery, with a particle mean diameter of 50 μm,and compressible.

Gas generants weighing 1.7 g were weighed and filled in the first hollowbody. Then, the gas generants were compressed for forming a concavityuntil the filling. volume was 1.89 cm³. The full volume of the gasgenerator is 2.3 cm³. The empty space calculated by the equation is40.41 cm³ and the ratio is 17.8% by volume. The weight of he gasgenerants per 1 cm³ of the filling volume is 0.9 g and the compressiondegree is 41.3%.

FIG. 3 shows the ratio of the empty space by volume and ignition delayperiod of the gas generator obtained in Example 2.

EXAMPLE 3

In the gas generator shown in FIG. 1, the spacer of 0.4 cm³ volume wasfixed around the second hollow body of the electric ignitor.

The same gas generants as those used in the Example 1 were employed. Thetrue density was 2.18 g/cm³. The gas generants were powdery, which witha particle mean diameter of 50 μm, and compressible. Gas generantsweighing 1.5 g were weighed and filled in the first hollow body. Then,the gas generants were compressed until the filling volume was 1.67 cm³.The full volume of the gas generator is 2.3 cm³. The empty spacecalculated by the equation is 0.23 cm³ and the ratio is 10.0% by volume.The weight of the gas generants per 1 cm³ of the filling volume is 0.9 gand the compression degree is 41.3%.

FIG. 3 shows the ratio of the empty space by volume and ignition delayperiod of the gas generator obtained in Example 3.

EXAMPLE 4

In the gas generator shown in FIG. 1, the spacer of 0.4 cm³ volume wasfixed around the second hollow body of the electric ignitor.

The gas generants containing 98.0% by weight of nitrocellulose, 1.0% byweight of diphenylamine, and 1.0% by weight of potassium sulfate wereemployed. The gas generants were incompressible, with particlespress-formed into a cylindrical shape having an outer diameter of 0.7mm, an inner diameter of 0.2 mm; and a height of 1.3 mm.

Gas generants weighing 1.3 g were weighed and filled in the first hollowbody. Then the gas generants were filled densely without compressionuntil the filling volume was 1.73 cm³. The full volume of the gasgenerator is 2.3 cm³. The empty space calculated by the equation is 0.17and the ratio is 7.4% by volume. The weight of the gas generants per 1cm³ of the filling volume is 0.75 g.

FIG. 3 shows the ratio of the empty space by volume and ignition delayperiod of the gas generator obtained in Example 4.

Comparative Example 1

The gas generator in the Comparative Example 1 is equivalent to the gasgenerator shown in FIG. 1 except the spacer is not included, and theratio of the empty space by volume is no less than 20%.

The same gas generants as those used in the Example 1 were employed. Thetrue density was 2.18 g/cm³. The gas generants were powdery, with aparticle mean diameter of 50 μm, and compressible.

Gas generants weighing 1.5 g were weighed and filled in the first hollowbody. Then, the gas generants were compressed until the filling volumewas 1.67 cm³. The full volume of the gas generator is 2.3 cm³. The emptyspace calculated by the equation is 0.63 cm³ and the ratio is 27.4% byvolume. The weight of the gas generants per 1 cm³ of the filling volumeis 0.9 g and the compression degree is 41.3%.

FIG. 3 shows the ratio of the empty space by volume and ignition delayperiod of the gas generator obtained in Comparative Example 1.

Generally, a permissible ignition delay period in seat beltpretensioners for automobiles is within 2 ms. When a delay more than 2ms occurs, an occupant restraint performance cannot be shownsufficiently.

According to FIG. 3. the ignition delay periods in Examples 1, 2, 3, 4are short being less than 2 ms. The ignition delay period in ComparativeExample 1 is substantially longer than 2 ms compared to those inExamples 1-4. Accordingly, it is shown that the ratio of the excessivespace i.e., the empty space in the first hollow body causes aconsiderable ignition delay of the gas generator.

INDUSTRIAL APPLICABILITY

The gas generator of the present invention is most suitable foractuating vehicle occupant restraint device, particularly, for a gasgenerator with a small component count, excellent in ignitability, andcapable of being miniaturized.

What is claimed is:
 1. A gas generator for actuating a vehicle occupantrestraint device comprising: a first hollow body with an end and a sidewall; gas generants filled densely in the first hollow body; an electricignitor formed by housing igniting agents in a second hollow body withan end and a side wall, and closing the second hollow body with a plug;and a holder positioning the second hollow body in a center of the firsthollow body and fixed to the first hollow body while holding the plug ofthe electric ignitor, wherein a ratio of an empty volume to a volumedefined by an inner surface of the first hollow body, an outer surfaceof the second hollow body, and the holder is less than 20%, a part of avolume is filled with a spacer inserted between the outer surface of thesecond hollow body and the inner surface of the first hollow body, andsaid spacer is made of a gas generant composition.
 2. The gas generatorfor actuating a vehicle occupant restraint device according to claim 1,wherein the gas generants are powdery or granulated, and filled in acompressed state.
 3. The gas generator for actuating a vehicle occupantrestraint device according to claim 1, wherein the gas generants aresubstantially incompressible.
 4. The gas generator for actuating avehicle occupant restraint device according to claim 1, wherein saidvolume ratio is less than 15%.
 5. The gas generator for actuating avehicle occupant restraint device according to claim 4, wherein saidvolume ratio is less than 10%.